ViewportGadget : Prefer NULL to 0
ViewportGadget : Prefer NULL to 0

So we can easily replace everything with nullptr when we find a time machine to take us forwards to 2011.

GafferHQ/gaffer,hradec/gaffer,ivanimanishi/gaffer,appleseedhq/gaffer,johnhaddon/gaffer,boberfly/gaffer,appleseedhq/gaffer,johnhaddon/gaffer,hradec/gaffer,ImageEngine/gaffer,johnhaddon/gaffer,GafferHQ/gaffer,GafferHQ/gaffer,appleseedhq/gaffer,GafferHQ/gaffer,hradec/gaffer,lucienfostier/gaffer,andrewkaufman/gaffer,boberfly/gaffer,ivanimanishi/gaffer,johnhaddon/gaffer,ImageEngine/gaffer,hradec/gaffer,GafferHQ/gaffer,ivanimanishi/gaffer,lucienfostier/gaffer,ImageEngine/gaffer,andrewkaufman/gaffer,lucienfostier/gaffer,ImageEngine/gaffer,andrewkaufman/gaffer,hradec/gaffer,andrewkaufman/gaffer,appleseedhq/gaffer,andrewkaufman/gaffer,boberfly/gaffer,lucienfostier/gaffer,johnhaddon/gaffer,ivanimanishi/gaffer,boberfly/gaffer